This invention relates generally to additive manufacturing processes and, in particular, to the formation of laminate structures using laser-assisted direct metal deposition processes
Fabrication of three-dimensional metallic components via layer-by-layer laser cladding was first reported in 1978 by Breinan and Kear. In 1982, U.S. Pat. No. 4,323,756 issued to Brown et al., describing a method for the production of bulk rapidly solidified metallic articles of near-net shape, finding particular utility in the fabrication of certain gas turbine engine components including discs and knife-edge air seals. According to the disclosure, multiple thin layers of feedstock are deposited using an energy beam to fuse each layer onto a substrate. The energy source employed may be a laser or an electron beam. The feedstock employed in the practice of the invention may be either a wire or powder material, and this feedstock is applied to the substrate in such a fashion that it passes through the laser beam and fuses to the melted portion of the substrate.
Different technologies have since evolved to improve such processes. U.S. Pat. No. 4,724,299 is directed to a laser spray nozzle assembly including a nozzle body with a housing that forms an annular passage. The housing has an opening coaxial with a passageway, permitting a laser beam to pass therethrough. A cladding powder supply system is operably associated with the passage for supplying cladding powder thereto so that the powder exits the opening coaxial with the beam.
Various groups are now working world-wide on different types of layered manufacturing techniques for fabrication of near-net-shape metallic components. In particular, nozzles of the type described above have been integrated with multi-axis, commercially available CNC machines for the fabrication of 3-dimensional components. U.S. Pat. No. 5,837,960 resides in a method and apparatus for forming articles from materials in particulate form. The materials are melted by a laser beam and deposited at points along a tool path to form an article of the desired shape and dimensions. Preferably the tool path and other parameters of the deposition process are established using computer-aided design and manufacturing techniques. A controller comprised of a digital computer directs movement of a deposition zone along the tool path and provides control signals to adjust apparatus functions, such as the speed at which a deposition head which delivers the laser beam and powder to the deposition zone moves along the tool path.
As a material for injection molds, thermally conductive materials such as copper and copper alloys have demonstrated significant performance improvements compared to the traditional use of tool steel alloys. The productivity improvement is associated with the increase in heat transfer due to the enhanced thermal conductivity of such materials.
The ability to fabricate articles comprised of high-density metallic materials using direct metal deposition becomes increasingly difficult as the thermal conductivity of the deposited material increases. Presently, laser-based deposition systems utilize either high-power CO2 or Nd-YAG lasers. As such, existing application of the technology do not include the fabrication of articles comprised of thermally conductive materials such as pure copper, or copper alloys. Instead, existing applications are relegated to the fabrication of three-dimensional articles comprised of iron- or cobalt-based alloys.
At the same time, the commercial applications of thermally conductive materials such as pure copper and related alloys are limited due to inferior material properties such as yield strength, hardness and abrasion resistance required for tools dies and molds. Moreover, the mechanical properties of copper and copper-based alloys are reduced significantly when they are exposed to elevated temperatures, inherent to the material being processed.
The use of copper and copper alloys as mold materials has accordingly been limited to low-temperature plastic injection molding applications associated with nonfilled polymers. Pure copper or copper-based alloys are typically not used as mold materials in metal die-cast or injection molding processes which include reinforced or glass-filled polymers, due to their relatively poor mechanical and physical properties.
This invention overcomes shortcomings in the prior art through the use of direct-metal deposition (DMD) to fabricate composite material structures which provide a combination of desirable physical and mechanical properties. In particular, use of the invention facilitates the production of high-strength, abrasion-resistant laminate structures which also exhibit a high degree of thermal conductivity.
In the preferred embodiment, the invention uses DMD to deposit alternate layers or rows of a thermally conductive material, such as copper or copper alloys, and a high strength, abrasion resistant thermal barrier material, such as tool steel. The resulting composite material structure has mechanical properties (i.e., yield strength, hardness and abrasion resistance) which exceed that of pure copper or copper-based alloys required for mold materials, thereby enhancing productivity while improving part quality in these and other applications.